The Romans founded Londinium (now called London) in 43 AD. This artist's illustration of Londinium in 200 AD shows the city's first bridge over the Thames River.

Westminster Abbey, built in the 10th century, is a World Heritage Site and one of London's oldest and most important buildings. Here it is in a 1749 painting.

Wikipedia Commons

William, Duke of Normandy, was crowned King of England there on Christmas Day, 1066 — just after it was completed.

By the 11th century, London had the largest port in England.

Getty Images

In the 12th century, the English royal court began to grow in size and sophistication, and settled in Westminster, a neighborhood in central London.

The Old Palace at Westminster.Wikipedia Commons

In 1176, King Henry II commissioned a new stone bridge. Finished in 1284, the original London Bridge would stand for over 600 years. It supported homes and shops — which weighed down its arches over time.

"View of London Bridge," a 1632 oil painting by Claude de Jongh.Wikipedia Commons

The development of the printing press in the early 15th century made news available to the entire city and improved literacy levels. Coffeehouses also became popular spots for friendly debates.

A London coffee house, circa 1660s.Public Domain

In the 17th century, London suffered from the Great Plague, which killed about 100,000 people. In 1666, the Great Fire broke out; it took the city a decade to rebuild.

Wikipedia Commons

The city became a major hub for trade throughout the 1700s, and the Port of London expanded downstream.

London Bridge, circa 1750.Wikipedia Commons

During the Georgian era (from 1714 to 1830), new districts like Mayfair formed, and new bridges over the Thames encouraged development in South London.

London's Trafalgar Square in 1814.Wikipedia Commons

In the mid-19th century, London overtook Amsterdam as the Europe's leading financial center ...

A London street, circa 1860s.James Hedderly

... and the Royal Navy became the world's leading military fleet.

London in the 19th century.Wikipedia Commons

London was the largest city in the world from 1831 until 1925, when New York City superseded it.